The present invention relates to a control method for engine valve actuation.
In U.S. Pat. No. 6,009,841, an engine with a hybrid valvetrain is disclosed in which one intake valve is actuated by a source other than a camshaft. This first intake valve is randomly operable meaning that the valve opening and closing events are independent of engine crankshaft operation, thus, a fully variable valve. A second intake valve is actuated by a camshaft and includes a deactivator. Operation of the second valve may be discontinued or restored within one engine cycle, termed selectable intake valve herein. The exhaust valve(s) of the hybrid valvetrain is conventionally camshaft actuated.
In U.S. Pat. No. 6,009,841, a method is described in which air is admitted using a randomly operable intake valve when the engine is operating when the engine is operating in a lowest range in torque, using a selectable intake valve when the engine is operating in a medium range in torque, and using both the randomly operable intake valve and the selectable intake valve when the engine is operating in a highest range in torque.
In U.S. Pat. No. 5,669,341, a method is described in which air is admitted through a smaller randomly operable intake valve when the engine is operating in a lowest range in engine speed, through a larger randomly operable intake valve when the engine is operating in a medium range in engine speed, and through both randomly operable intake valves when the engine is operating in a highest range in engine speed.
In U.S. Pat. No. 5,647,312, a method is described in which air is admitted using a randomly operable intake valve when the engine is operating in a lower range in torque and speed and air is admitted using a selectable intake valve when the engine is operating at higher speed or higher torque. The determination of which valves to actuate is based on predetermined rpm and engine torque levels.
The inventors herein have recognized disadvantages of the approaches of U.S. Pat. Nos. 6,009,841, 5,647,312 and 5,669,341. Operation according to ""841 may lead to combustion harshness due to excessive turbulence in the air charge when it is admitted solely through a smaller randomly operable valve at a condition of low engine torque and high engine speed. The method taught in patent ""341 limits engine torque by admitting fresh air through only a smaller intake valve at a lowest engine speed and through a larger intake valve through a medium engine speed. The inventors herein have recognized that such an approach may result in combustion harshness and a lesser peak torque than could be realized because it limits airflow by inducting it through a single valve at the lowest and medium engine speeds. Finally, the inventors herein have recognized that operation according to ""312 limits engine torque at all engine speeds by teaching that fresh air is admitted only through the selectable intake valve. Another disadvantage of ""312 is that the criteria for making a transition among operating modes is based on a predetermined rpm and a predetermined torque, the determination of which is not disclosed. The inventors herein have recognized that predetermined rpm and torque are arbitrary criteria.
A method is provided for operating an internal combustion engine, with the engine having at least one cylinder, at least one randomly operable intake valve, at least one selectable intake valve with a predetermined valve closing time, a throttle valve in the intake system, and an engine control unit. The method provides the steps of sensing demanded engine torque and engine speed. Further steps include admitting air into the cylinder through the randomly operable intake valve when the engine is operating in a first region characterized by a first relationship between engine speed and engine torque, admitting air into the cylinder through the selectable intake valve when the engine is operating in a second region characterized by a second relationship between engine speed and engine torque, wherein for a given engine torque the second region provides a higher engine speed than the first region, and admitting air into the cylinder through both the randomly operable intake valve and the selectable intake valve when the engine is operating in a third region characterized by a third relationship between engine speed and engine torque, wherein for a given engine speed the third region provides a higher engine torque than the first and second regions.
An advantage of the method disclosed herein is that it lowers the turbulence level of the admitted charge by admitting air through a valve other than a smaller valve at higher engine speed, thereby overcoming combustion harshness of prior art methods.
To provide maximum air flow to achieve the highest engine torque, air must be admitted through all intake valves. Thus, a further advantage of the present invention is to provide a high peak engine torque at all engine speeds.
Other advantages, as well as objects and features of the present invention, will become apparent to the reader of this specification.